In conventional furnaces for growing crystals a crucible is placed inside a furnace chamber. In order to form a crystal component, a seed crystal is arranged inside the crucible. The seed crystal is generally made of a desired crystal material which is the material of the crystal component to be formed. The furnace is heated up such that a crystal material inside the crucible is provided in a molten and liquid state.
The crystal component is formed by growing the crystal component starting from the seed crystal at the bottom of the crucible. In order to achieve a crystal growing from the bottom of the crucible, the temperature of the bottom of the crucible has to be controlled exactly, so as not to melt the seed crystal and so that the already grown solid crystal component will not become liquid again due to temperature variations. The bottom of the furnace should therefore be cooler than the top, preferably with a stabilizing temperature gradient that minimizes convection. The material in the crucible can solidify from the bottom to the top due to the vertical temperature gradient.
In conventional furnace systems it is known to use a cooled crucible shaft and/or movable temperature shields in order to cool the bottom section of the crucible and the crystal component which has already been formed. By the cooled shaft or temperature shields, a controlled solidification of the crystal liquid in the crucible from the bottom upwards may be controlled and a desired temperature gradient in the crucible may be provided. Furthermore, it is known to extract heat from the bottom of the furnace.